Crocodile Tears Syndrome

Etiology

There are different theories regarding the cause of crocodile tears syndrome. The widely accepted theory is due to Bell palsy or traumatic disruption of the nervus intermedius.

Epidemiology

Bell palsy is facial nerve palsy leading to facial muscle weakness due to an unknown cause. Nemet et al. found the incidence of Bells Palsy to be 0.08% per year, and usually, the incidence increases with age (fourth to sixth decades of life).[3] In a study published by Valenca et al, women were found to be more affected by Bell palsy, and the left eye was more frequently involved as compared to the right.[4] Crocodile tears syndrome is a complication occurring of Bell palsy with an incidence of 3.3%.[4] As stated by Yamamoto et al, crocodile tears syndrome occurs approximately 6 to 9 months after Bell palsy.[5]

Pathophysiology

In the recovery period following facial nerve injury, the regenerating salivary nerve fibers undergo synkinesis or are misdirected to ultimately innervate the lacrimal gland instead of the submandibular gland. As shown in the figure below, the regenerating nerves are directed toward the lacrimal gland via the greater superficial petrosal nerve. The result is that any stimuli, such as the smell or taste of food, instead of causing salivation, excites the lacrimal gland to produce ipsilateral tearing.[6]

Another theory put forth by Spiers et al. is a congenital abnormality. The finding supported this that few patients with crocodile tears syndrome also had underlying lateral rectus palsy or co-existing with Duane retraction syndrome. It was suspected that the lesion was in the pons adjacent to the abducens nerve.[6] Another mechanism for crocodile tears syndrome is thought to be the formation of an artificial synapse at the injury site. This synapse allows the impulses to jump from one fiber to another, and crossovers are likely, leading to crocodile tears syndrome.[7]

History and Physical

Crocodile tears syndrome involves unilateral lacrimation or tearing whenever the patient eats or drinks. However, bilateral cases have also been recorded by Speirs et al.[6] On clinical and slit-lamp examination of the eye and the lacrimal appendages, it appears within normal limits. This rules out other causes of epiphora, such as lacrimal duct obstruction, chronic dacryocystitis, punctal stenosis, conjunctivitis, and foreign body in the conjunctiva. Crocodile tears syndrome is mostly a diagnosis of exclusion in patients with a prior history of facial nerve palsy. Patients with a previous incidence of Bell palsy may have a history of acute-onset symptoms of neck, mastoid, or ear pain, altered taste or facial sensation, and hyperacusis.

Evaluation

Crocodile tears syndrome is a diagnosis of exclusion. Slit lamp examination of the eye and appendages is usually done to rule out other causes of epiphora. The basal tear secretion of an individual can be assessed by using Schirmer's test. In the case of crocodile tears syndrome, it can be performed before and after gustatory stimulation to document increased tearing after salivation. It is also important to rule out other differentials.

• Orbicularis oculi weakness due to facial palsy: The orbicularis oculi muscle is tested by asking the patient to shut his or her eyes tightly while the examiner tries to open them. The force required to open the eyelid can be graded, and accordingly, the degree of muscle weakness can be ascertained.
• Paralytic ectropion: The examiner performs the snap-back test to check for lower lid laxity. A positive test is obtained when the eyelids spring back immediately into their original position after being pulled down by the examiner.
• Nasolacrimal duct obstruction: ROPLAS (regurgitation on pressure over lacrimal sac) test is used to ascertain nasolacrimal duct obstruction.

Treatment / Management

Historically, many different treatment options have been used to stop lacrimation. A 5% solution of guanethidine was used to block the adrenergic receptors in the lacrimal gland.[6] Peroral treatment with propantheline bromide 30 mg was also tried.[6] It was also believed that instilling 1% homatropine hydrobromide in the conjunctival sac would lead to secretomotor nerve blockade.[6] However, the side effects of these pharmacological modulations outweighed their therapeutic outcome, and thus, presently, they are not the preferred line of treatment. (B3)

Surgical options include excision of the palpebral lobe of the lacrimal gland, cutting of the chorda tympani nerve, denervation of the lacrimal gland either by dissection or diathermy, and sphenopalatine ganglion blockage by alcohol or cocaine, and vidian neurectomy.[6] Nevertheless, these options are redundant, drastic, and have persistent adverse events such as vision loss and total ablation of the lacrimal gland.(B3)

The treatment of crocodile tears syndrome depends on the severity of the hyperlacrimation and the need of the patient. Mild cases are generally managed by counseling and regular monitoring. Less drastic surgical options are used, and they are proving to be an effective way to control the tearing. Subtotal resection of the palpebral lobe of the lacrimal gland is considered beneficial by McCoy et al., and pre-operative Schirmer’s test helps to control the amount of gland to be resected and thus prevent dry eye.[1]  (B3)

The most widely accepted treatment of crocodile tears syndrome is botulinum toxin injection into the lacrimal gland.[8] Botulinum toxin-A is an acetylcholine release inhibitor and acts at the neuromuscular junction. It acts by stopping transmission along the aberrantly regenerated parasympathetic nerve fibers to the affected gland. It can be administered both transcutaneously and transconjunctivally to the lacrimal gland in crocodile tears syndrome patients.[7] The botulinum toxin dose injected into the lacrimal gland is 2.5 units, and its effect lasts for around 6 months.[8] The transconjunctival route of injection into the palpebral route is proven to have fewer complications than injecting transcutaneously. Montoya et al. report that the injection of botulinum toxin into the lacrimal gland in crocodile tears syndrome is a safe and effective method for treating excessive tearing.[7](B3)

Differential Diagnosis

The diagnosis of crocodile tears syndrome should be considered after excluding common differential diagnoses such as simple epiphora following Bell palsy.[9] This occurs due to loss of tone of the orbicularis oculi muscle, which leads to sagging of the lower eyelid. As the lower lid is not apposed to the eye, the normal tears cannot drain through the punctum, and they spill over, resulting in the watering of the eye.

Other differentials include nasolacrimal duct obstruction, conjunctivitis, and allergies. These conditions are not associated with hyperlacrimation, and typically the patient will give no history of increased tearing while eating food. Furthermore, in crocodile tears syndrome, the clinical examination of the eye and its appendages will be within normal limits. Also, a latency of 6 months is usually present between the onset of facial nerve palsy and crocodile tears syndrome for the nerves to regenerate.[9]